This invention relates to dispensers for volatile materials in liquid form, in particular for releasing such materials into the surrounding atmosphere.
The release of volatile liquids, e.g. of air freshening materials and fragrances, into the atmosphere over a period of time can be achieved in a number of ways. Where a slow sustained dispersal of the material is required, it is known to expose a porous pad impregnated with the material or to provide a liquid reservoir from which a wick protrudes to draw up liquid from the reservoir, the liquid then evaporating from the exposed surface of the wick. These known dispersal methods have the advantage of low cost but they have a failing if the material to be dispersed is a mixture of substances with different volatilities, as is typical of fragrances. The components with greater volatility then escape more readily than those with lower volatility with the result that the character of the fragrance changes markedly over the period of use, which is clearly undesirable. If an impregnated porous pad is used, there is the further disadvantage that it cannot be readily seen when the volatile material is about to be exhausted.
According to one aspect of the present invention, there is provided a dispenser for a volatile liquid comprising at least one dispersal screen in which a series of threads run in one direction with spaces between at least some of the threads, a liquid reservoir in communication with the screen, the individual threads and/or closely grouped pluralities of threads of said series between said spaces being arranged to exert a capillary action on liquid reaching the screen from the reservoir.
Such a dispersal screen is able to offer a generally laminar and permeable base over which a material to be released can readily diffuse, e.g. by capillary action. The spaces between said threads increase the exposure of the liquid to the surrounding atmosphere and allow a flow of air to be induced through the screen to increase the rate of dispersal. Preferably, said spaces are at least equal to the thickness of the threads or groups of threads, and to enhance these effects it can be arranged that said spaces are equal to several times that thickness.
The screen can have a very low bulk in comparison to the area exposed to the atmosphere so that the amount of liquid taken up from the reservoir onto the screen at any moment is limited and is relatively quickly dispersed. It can therefore be arranged that the rate at which the components with higher volatility are exposed is restricted, as compared with a prior art pad, while less opportunity for components with lower volatility to accumulate on the screen, whereby a more even dispersal of the liquid over a period of time can be achieved.
In a preferred form of screen, said series of threads is interwoven with a second series of threads running transversely thereto, the threads of said second series being spaced so as to provide a void ratio transverse to the direction in which they run that is preferably at least as great as that provided by the spaces between the threads or groups of threads of the first series.
According to a further aspect of the present invention, there is provided a dispenser for a volatile to material comprising a reservoir for containing the material as a liquid, and a dispersal screen from which the material can evaporate or volatilise into the surrounding atmosphere, said screen being in communication with the liquid in the reservoir and comprising a fabric having first and second series of threads running in mutually transverse directions, at least in one of said directions the threads being arranged in spaced groups in which the threads of a group are more closely spaced than in the spaces between the groups, said groups of threads being arranged to exercise a capillary action an the liquid reaching the screen from the reservoir to promote diffusion of the liquid over the screen.
The screen can be arranged with threads dipping into the liquid in the reservoir to draw the liquid over the screen surface. There can however be advantages in employing an intermediate transfer device, e.g. a member providing a plurality of capillary passages such as a wick, to take up the liquid from the reservoir and carry it to the screen. Preferably, the transfer device is shielded from exposure to the atmosphere, to ensure that there is no significant volatilisation of the liquid before it reaches the screen.
The screen can be mounted in a rigid surrounding frame. It can be composed of more than one layer having said series of threads, but if there are a multiplicity of layers it is desirable to ensure that their combined effect does not unduly impede air flow through the screen, in order to limit the time between the liquid reaching the screen and it being released into the surrounding atmosphere. It is also possible to supply a plurality of dispersal screens from a common reservoir.
It is generally desirable to employ gravitational effects to complement capillary forces acting on the liquid, the liquid thus being supplied to the upper region of a downwardly extending screen. Such an arrangement can give a more even spread of liquid over the screen, so enhancing the rate of evaporation. The screen may be so arranged that the gravitational forces produce a syphon effect drawing the liquid from a reservoir below the top of the screen onto the top of the screen. Although capillary forces may be relied on to draw the liquid onto the screen, once the syphon effect has been established and the flow path onto the screen has become saturated, the capillary effect will cease to have any influence. Flow is continued through the action of intermolecular and gravitational forces until the liquid path is broken. In addition, by locating the bottom of the screen below the liquid level in the supply reservoir a hydrostatic bias can be established that ensures the flow is maintained.
Thus, according to another aspect of the invention, there is provided a dispenser for a volatile liquid comprising a reservoir for the liquid and a fluid conduit providing a flow path extending upwardly from the reservoir to an upper region of a downwardly extending laminar dispersal or diffusion screen, said fluid conduit having means for drawing liquid from the reservoir to said upper region to allow the liquid to flow by gravity down the screen as it is dispersed therefrom.
The laminar screen is preferably of a form that holds only a small amount of liquid at any instant, for example having the structure described above, although other screen materials may be employed. Under optimum conditions it may be arranged that the liquid will disperse completely from the screen before it reaches the bottom of the screen. In practice, however, it may be desirable to provide a lower marginal region with a greater liquid absorption capacity than the higher regions of the screen, to hold any surplus of liquid that has not volatilised before reaching the lower region. Liquid can thus be retained in the lower region in adverse operating conditions, for example if there is a drop of temperature below the average, as it disperses more slowly. Additionally or alternatively the surplus liquid can be arranged to be transferred to a further dispersal element. In these ways, lower volatile components can be drawn off the main area of the screen so as not to block the flow of higher volatility components onto the screen.
If a dispenser according to the invention has a fluid circuit which provides an upwardly extending flow path from a reservoir of liquid to be dispersed to the top region of a screen to allow the liquid to be exposed to the surrounding atmosphere as it flows down the screen, it may be arranged that the liquid level in the reservoir is maintained substantially constant to give a more uniform conditions along the liquid path to the top of the screen.
In one arrangement having this characteristic, the dispenser may comprise a reservoir chamber for the liquid having an opening to the atmosphere and located below a container having a bottom outlet below the level of said opening for supplying liquid to the reservoir chamber, in the reservoir chamber an outlet conduit extending from a level below said container outlet for leading liquid from the chamber to the screen, whereby lowering of the liquid level in the chamber below said level of the supply container bottom outlet by the removal of liquid through said conduit allows further liquid to flow from the container into the chamber to maintain the liquid level therein.
The reservoir chamber may be supplied by a liquid container in the form of a replaceable sealed container, and means may be provided for placing the container in communication with the chamber automatically as it is mounted in place on the dispenser. Thus, a piercing element may project upwardly from the chamber, into a socket into which the supply container is sealingly inserted, the bottom of the container being pierced as it is inserted.
In an alternative embodiment, a refillable supply container is provided. If it is open to atmosphere during the filling, means are required to prevent the liquid simply flowing through the container and draining from the bottom outlet into the reservoir. In one preferred form, the container is provided with coupled inlet and outlet valves by means of which, when the inlet valve is opened to allow filling, the outlet valve is automatically closed to seal the supply container from the reservoir.
As an alternative to attempting to maintain uniform supply conditions to the screen, or in addition thereto, it may be arranged that the amount of liquid on the screen determines the supply of further liquid to the top of the screen, so as to limit the amount on the screen at any instant. This may be a preferred method of operation if there are significant fluctuations in the rate of dispersal from the screen, e.g. due to changes of ambient temperature. In particular, the amount of liquid held by the screen at any moment may be limited by providing an arrangement that interrupts the supply of further liquid to the screen in dependence upon the amount already present,
Thus, in one form of such an arrangement, the screen is displaceably supported in a manner allowing it to move in dependence upon the weight of liquid it holds, such that said movement displaces the screen to interrupt the fluid conduit flow path when the weight exceeds a permitted maximum. If liquid continues to disperse from the screen after the flow path has been interrupted, the screen can return to its previous position when it has been sufficiently lightened, and it can be arranged that the return displacement re-establishes the flow path, so that the supply of liquid to the screen begins again.
This process can be accelerated by removing excess liquid from the screen. For example, an absorbent holding element may be located adjacent the screen to come into contact with said lower region when the screen is displaced by the weight of excess liquid. Some of the liquid in the lower region of the screen can then flow onto the holding element, which may itself be in the form of a sheet or mat providing a dispersal surface from which the liquid can volatilise, albeit more slowly. With a fragrance having a mixture of constituents of different volatilities, the accumulated liquid will usually consist wholly or mainly of the less volatile constituents, and the removal of this liquid with re-establishment of the flow of fresh liquid to the screen ensures continuance of the supply of the more volatile components so that the sensed character of the fragrance is maintained more uniform.